Multi quantizer loops for delta-sigma converters

ABSTRACT

The number of bits in the quantizer can be decoupled from the number of bits in the feedback digital-to-analog converter (DAC) A delta-sigma analog-to-digital converter circuit can include a first quantizer to generate an output having a first number of bits and a second quantizer coupled to an output of the first quantizer, where the second quantizer can receive the output of the first quantizer and generate an output having a second number of bits. The feedback DAC can be coupled to the second quantizer to receive a representation of the output of the second quantizer, where the output of the feedback digital-to-analog converter circuit has the second number of bits. These techniques can reduce the area of the feedback DAC, e.g., 4 or 5 bits, and the techniques can achieve a higher maximum stable amplitude (MSA) because it is effectively a second order loop.

FIELD OF THE DISCLOSURE

This document pertains generally, but not by way of limitation, todigital-to-analog conversion, and more particularly to delta-sigmaconverter circuits.

BACKGROUND

In many electronics applications, an analog input signal is converted toa digital output signal (e.g., for further digital signal processing).For instance, in precision measurement systems, electronics are providedwith one or more sensors to make measurements and these sensors cangenerate an analog signal. The analog signal can then be provided to ananalog-to-digital converter (ADC) circuit as input to generate a digitaloutput signal for further processing. In another instance, in a mobiledevice receiver, an antenna can generate an analog signal based on theelectromagnetic waves carrying information/signals in the air. Theanalog signal generated by the antenna can then be provided as input toan ADC to generate a digital output signal for further processing.

SUMMARY OF THE DISCLOSURE

This disclosure is directed to, among other things, techniques todecouple the number of bits in a quantizer from the number of bits inthe feedback digital-to-analog converter (DAC). A delta-sigmaanalog-to-digital converter circuit can include a first quantizer togenerate an output having a first number of bits and a second quantizercoupled to an output of the first quantizer, where the second quantizercan receive the output of the first quantizer and generate an outputhaving a second number of bits. The feedback DAC can be coupled to thesecond quantizer to receive a representation of the output of the secondquantizer, where the output of the feedback digital-to-analog convertercircuit has the second number of bits. These techniques can reduce thearea of the feedback DAC, e.g., 4 or 5 bits, and the techniques canachieve a higher maximum stable amplitude (MSA) because it iseffectively a second order loop.

In some aspects, this disclosure is directed to a delta-sigmaanalog-to-digital converter circuit to receive an analog input signal atan input and generate a digital output signal, the delta-sigmaanalog-to-digital converter circuit comprising: an input summing nodeconfigured to receive and combine the analog input signal and an outputof a digital-to-analog converter circuit; a first quantizer to receive arepresentation of the combined analog input signal and output of thedigital-to-analog converter circuit, the first quantizer to generate anoutput having a first number of bits; a second quantizer coupled to anoutput of the first quantizer to receive the output of the firstquantizer, the second quantizer to generate an output having a secondnumber of bits; and the digital-to-analog converter circuit coupled tothe second quantizer to receive a representation of the output of thesecond quantizer, wherein the output of the digital-to-analog convertercircuit has the second number of bits.

In some aspects, this disclosure is directed to a method of operating adelta-sigma analog-to-digital converter circuit to receive an analoginput signal at an input and generate a digital output signal, themethod comprising: receiving and combining, using an input summing node,the analog input signal and an output of a digital-to-analog convertercircuit; receiving, using a first quantizer, a representation of thecombined analog input signal and output of the digital-to-analogconverter circuit and generating an output having a first number ofbits; receiving, using a second quantizer coupled to an output of thefirst quantizer, the output of the first quantizer and generating anoutput having a second number of bits; and receiving, using thedigital-to-analog converter circuit coupled to the second quantizer, arepresentation of the output of the second quantizer, wherein the outputof the digital-to-analog converter circuit has the second number ofbits.

In some aspects, this disclosure is directed to a delta-sigmaanalog-to-digital converter circuit to receive an analog input signal atan input and generate a digital output signal, the delta-sigmaanalog-to-digital converter circuit comprising: an input summing nodeconfigured to receive and combine the analog input signal and an outputof a digital-to-analog converter circuit; a successive approximationregister analog-to-digital converter to receive a representation of thecombined analog input signal and output of the digital-to-analogconverter circuit, the successive approximation registeranalog-to-digital converter to generate an output having a first numberof bits; a digital quantizer coupled to an output of the successiveapproximation register analog-to-digital converter to receive the outputof the successive approximation register analog-to-digital converter,the digital quantizer to generate an output having a second number ofbits; and the digital-to-analog converter circuit coupled to the digitalquantizer to receive a representation of the output of the digitalquantizer, wherein the output of the digital-to-analog converter circuithas the second number of bits.

This summary is intended to provide an overview of subject matter of thepresent patent application. It is not intended to provide an exclusiveor exhaustive explanation of the invention. The detailed description isincluded to provide further information about the present patentapplication.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIG. 1 is a schematic block diagram of an example of a data acquisitionsystem 10, which can implement a delta-sigma modulator.

FIG. 2 is a block diagram of an example of a first-order single-bitdelta-sigma ADC.

FIG. 3 is a block diagram of an example of a delta-sigma ADC circuitthat can implement various techniques of this disclosure.

FIG. 4 is a graph of an example of a simulation comparing outputspectrums.

FIG. 5 is a graph of another example of a simulation comparing outputspectrums.

FIG. 6 is a block diagram of another example of a delta-sigma ADCcircuit that can implement various techniques of this disclosure.

DETAILED DESCRIPTION

In existing delta-sigma analog-to-digital converter (ADC) approaches,the number of bits in the quantizer typically dictates the number ofbits in the feedback digital-to-analog converter (DAC). The size of thefeedback digital-to-analog converter can become a limiting factor,however. For example, using more than six bits in the quantizer can makethe feedback DAC prohibitively large, or even require multiple feedbackDACs, such as due to the thermometer coding used by the feedback DAC.

Some delta-sigma ADC approaches use splitter techniques or segmentationtechniques to reduce the effective number of bits in the feedback DAC.Segmentation techniques can cause errors, however, such as gainmismatch. For example, errors between the most significant bits (MSBs)and the least significant bits (LSBs) can be problematic.

Some delta-sigma ADC approaches use a finite impulse response (FIR) DACtechnique. In such an approach, a 1-bit quantizer can be used with amulti-bit feedback DAC, where FIR filtering can be used to convert asingle bit to multiple bits that can be received by the feedback DAC.

In existing approaches, the number of bits in the quantizer dictatesboth the in-band noise and the out-of-band noise. There is noindependent control of the in-band noise and the out-of-band noise; onecan be improved but at the expense of the other.

There are several techniques that can be used to improve the signal toquantization noise ratio (SQNR) in delta-sigma ADCs. Some delta-sigmaADC approaches use a higher oversampling rate (OSR), such as 128 or 256for audio applications. However, the higher OSR can affect amplifierbandwidths and increase power consumption, although passive area can bereduced.

In another delta-sigma ADC approach, higher order architectures, such asthird order or higher, can be used. However, the maximum stableamplitude (MSA) can be reduced and there can be instability issues. Inaddition, the area is larger-even with single operational amplifierresonator circuits because the passive driven area increases.

In another delta-sigma ADC approach, the infinity value can beincreased, which is a proxy for more out-of-band noise. However, ahigher H infinity value is typically not a good way to achieve adesirable SQNR; as H infinity is increased, the more impact it can haveon stability and jitter, for example.

Using various techniques of this disclosure, the number of bits in thequantizer can be decoupled from the number of bits in the feedback DAC.As described in detail below, a delta-sigma analog-to-digital convertercircuit can include a first quantizer to generate an output having afirst number of bits and a second quantizer coupled to an output of thefirst quantizer, where the second quantizer can receive the output ofthe first quantizer and generate an output having a second number ofbits. A feedback digital-to-analog, converter circuit can be coupled tothe second quantizer to receive a representation of the output of thesecond quantizer, where the output of the feedback digital-to-analogconverter circuit has the second number of bits. These techniques canallow the first quantizer to generate an output having a large number ofbits and can keep the loop order and the OSR low, e.g., second order and64×OSR for audio applications. In addition, the area of the feedbackdigital-to-analog converter circuit can be reduced, e.g., 4 or 5 bits,and the techniques can achieve a higher maximum stable amplitude (MSA)because it is effectively a second order loop.

FIG. 1 is a schematic block diagram of an example of a data acquisitionsystem 10, which can implement a delta-sigma modulator. The dataacquisition system 10 can be an electronic device (including anelectronic circuit and/or one or more components) configured to convertsignals (such as analog signals) into a usable form. In variousimplementations, the data acquisition system 10 can convert physicalconditions into digital form, which can be stored and/or analyzed. FIG.1 has been simplified for the sake of clarity. Additional features canbe added in the data acquisition system 10, and some of the featuresdescribed can be replaced or eliminated in other embodiments of the dataacquisition system 10.

In FIG. 1 the data acquisition system 10 can include an input signal 15that represents a physical condition, such as temperature, pressure,sound, velocity, flow rate, position, other physical condition, orcombination thereof. A sensor circuit block 20 can receive an inputsignal 15 and convert the physical condition (represented by inputsignal 15) into an electrical signal, such as an analog signal 25. Theanalog signal 25 can be a voltage or current that represents thephysical condition (represented by the input signal 15).

A signal conditioning circuit block 30 can receive and adjust the analogsignal 25 within an acceptable range of an analog-to-digital converter(ADC), providing a conditioned analog signal 35. The conditioned analogsignal 35 can be provided at ADC circuit block 40, such that the signalconditioning circuit block 30 can act as an interface between the sensorcircuit block 20 and the ADC circuit block 40, the conditioning analogsignal 25 (and thus providing the conditioned analog signal 35) beforethe ADC circuit block 40 digitizes the analog signal. The signalconditioning circuit block 30 can amplify, attenuate, filter, and/orperform other conditioning functions to the analog signal 25. The ADCcircuit block 40 can receive and convert the conditioned analog signal35 into digital form, providing a digital signal 45. The digital signal45 can represent the physical quantity received by the sensor via theinput signal 15. A digital signal processor (DSP) circuit block 50 canreceive and process digital signal 45.

The ADC circuit block 40 can include a delta-sigma ADC that generates adigital signal using a feedback technique, where the delta-sigma ADC canoversample its input signal (here, the conditioned analog signal 35) andperform noise-shaping to achieve a high-resolution digital signal (here,the digital signal 45). The delta-sigma ADC can include a delta-sigmamodulator 60 and a digital filter/decimator 70. The delta-sigmamodulator 60 can use oversampling (for example, a sampling rate aboveNyquist rate) and filtering to generate a digital signal that representsthe input signal received by the delta-sigma ADC (such as theconditioned analog signal 35).

In various implementations, the delta-sigma ADC feedback loop forces theoutput of the modulator to be a good representation of the input signalin the bandwidth of interest. The digital filter/decimator 70 canattenuate noise and/or slow a data rate (for example, to a Nyquistsampling rate) of the digital signal, providing the digital signal 45.The digital filter/decimator 70 can include a digital filter, adecimator, or both. The digital filter can attenuate the digital signalreceived from the delta-sigma modulator 60, and the decimator can reducea sampling rate of the digital signal received from the delta-sigmamodulator 60.

FIG. 2 is a block diagram of an example of a first-order single-bitdelta-sigma ADC. The delta-sigma modulator 100 can be an example of thedelta-sigma modulator 60 of FIG. 1 . The delta-sigma modulator 100 canconvert an input signal (Vin) into a continuous serial stream of onesand zeros at a rate determined by a sampling clock frequency Kfs. Aone-bit digital-to-analog converter (DAC) 102 can be driven by theserial output data stream to generate a feedback signal. The output ofthe digital-to-analog converter (DAC) 102 can be subtracted from theinput signal using a summing element 104. The summing element 104 can beimplemented as the summing node of an operational amplifier (op amp),such as the op amp of an integrator 106.

The integrator 106 can integrate the output of summing element 104, andthe output of the integrator 106 can be applied to a clocked latchedcomparator 108. For an input signal of zero, the comparator output caninclude an approximately equal number of ones and zeros. For a positiveinput voltage, the comparator output contains more ones than zeros. Fora negative input voltage, the comparator output contains more zeros thanones. The average value of the comparator output over a number of cyclesrepresents the input voltage. The comparator output can be applied to adigital filter and decimator 110 that averages every M cycles, where Mis a positive integer greater than 1. The digital filter and decimator110 can be an example of the digital filter/decimator 70 of FIG. 1 . Thedecimator reduces the effective sampling rate at the output to fs.

FIG. 3 is a block diagram of an example of a delta-sigma ADC circuitthat can implement various techniques of this disclosure. In the exampleshown, the circuit 200 can be a second order feed-forward loop having afirst integrator 202 and a second integrator 204. The first integrator202 and the second integrator 204 can be continuous time integrators ordiscrete time integrators, e.g., switched capacitor-based integrators.The circuit 200 can receive an analog input signal 206 at an input 208,e.g., a buffer. An input summing node 210 can receive and combine theanalog input signal 206 and an output of a feedback digital-to-analogconverter circuit 212.

The first integrator 202 can receive the output of the input summingnode 210 and perform an integration. The output of the first integrator202 can be applied to a gain block 214, and the output of the gain block214 can be combined with the output of the second integrator 204 by asumming node 216. The first integrator 202 and the second integrator 204form a second order loop filter. In other examples, there can be oneintegrator, e.g., a first order loop filter, or more than twointegrators. As such, the loop filter can be any order loop filter.

As mentioned above, the circuit 200 can include a first quantizer 218and a second quantizer 220, The first quantizer 218 can receive theoutput of the summing node 216, which can be a representation of thecombined analog input signal 206 and output of the digital-to-analogconverter circuit 212. The first quantizer 218 can generate an outputhaving a first number of bits. As a non-limiting example, the firstquantizer 218 can generate an output having 8-10 bits.

The first quantizer 218 can dictate the in-band signal-to-quantizationnoise ratio (SQNR) of the circuit 200. In some examples, the firstquantizer 218 can be a flash ADC. In some examples, the first quantizer218 can be a successive approximation register (SAR) ADC circuit, suchas an asynchronous SAR ADC or a synchronous SAR ADC.

In accordance with this disclosure, the circuit 200 can further includea second quantizer 220 coupled to an output of the first quantizer 218to receive the output of the first quantizer 218. The second quantizer220 can generate an output having a second number of bits. In someexamples, the second number of bits is less than the first number ofbits. As a non-limiting example, the second quantizer 220 can generatean output having 4 or 5 bits.

In some examples, the second number of bits of the second quantizer 220can be less than the first number of bits of the first quantizer 218. Insome examples, the second quantizer 220 can be implemented using digitaltechniques, such as a processor circuit, such as a digital signalprocessor circuit.

In the example shown, an output of the first quantizer 218 can be fed toa second quantizer summing node 222. The second quantizer 220 canreceive an output of the second quantizer summing node 222, which canalso be applied to a summing node 224. The output of the secondquantizer 220 can be applied to the summing node 224 and subtracted fromthe output of the second quantizer summing node 222, In addition, theoutput of the second quantizer 220 can be applied to an output node 226of the circuit 200 to provide a digital output of the delta-sigma ADC.

An output of the summing node 224 can be applied to a filter F(z), e.g.,a finite impulse response (FIR) filter, which can then be fed to thesecond quantizer summing node 222 during the next clock cycle. Thefilter F(z) can receive a difference between an input of the secondquantizer 220 and the output of the second quantizer 220. The filterF(z) can be a first order filter or a higher order filter. In someexamples, the filter F(z) can be a delay such as z⁻¹. The output of thefilter F(z) can be combined with the output of the first quantizer bythe second quantizer summing node 222.

In configurations in which the first quantizer 218 is a SAR ADC, anexcess loop delay compensation circuit 228 can be included. The excessloop delay compensation circuit 228 can include a filter 230, e.g., adelay such as z⁻¹, and a gain block 232, for example. The output of theexcess loop delay compensation circuit 228 can be fed to the secondquantizer summing node 222 and subtracted from the other two inputs tothe second quantizer summing node 222. The excess loop delaycompensation circuit 228 can receive an output of the second quantizer220 and compensate for a delay introduced by the first quantizer 218.The second quantizer summing node 222 can receive an output of theexcess loop delay compensation circuit 228, an output of the filterF(z), and the output of the first quantizer 218.

This technique of using a second quantizer 220 can re-quantize theoutput of the first quantizer 218 in order to reduce the number of bitsapplied to the feedback digital-to-analog converter circuit 212. In thismanner, the circuit 200 can include a multi-quantizer loop (MQL).Although two quantizers are shown, more than two quantizers can be used.In such a configuration, the number of bits can be reduced in stages,such as from 8 bits to 5 bits to 3 bits by using three quantizers in anon-limiting example.

The output of the second quantizer 220 can be fed to a buffer 234 andthe output of the buffer can be fed to a filter 236, e.g., a delay suchas z¹, such as in configurations in which the first quantizer 218 is aSAP ADC. For example, the filter 236 can provide one clock delay toemulate the delay of a SAR ADC or for dynamic element matching. Thefilter 236 can be coupled to an input of the feedback digital-to-analogconverter circuit 212. As a non-limiting example, the first quantizer218 can generate an output having 8-10 bits and the feedbackdigital-to-analog converter circuit 212 can generate an output having 4or 5 bits. In this manner, the feedback digital-to-analog convertercircuit 212 can be coupled to the second quantizer 220 to receive arepresentation of the output of the second quantizer 220, where theoutput of the feedback digital-to-analog converter circuit 212 has thesecond number of bits.

By using both the first quantizer 218 and the second quantizer 220, thecircuit 200 can decouple the in-band SQNR and out-of-band energy, incontrast to existing approaches. In addition, the number of bits in thefirst quantizer 218 can be decoupled from the number of bits in thefeedback digital-to-analog converter circuit 212. This can allow thefeedback digital-to-analog converter circuit 212 to be much smaller thanin existing approaches. For example, the feedback digital-to-analogconverter circuit 212 can fewer elements. As an example, a thermometerencoded digital-to-analog converter circuit can have 2^(N) elements. Areduction in the number N from 8 bits to 5 bits can reduce the number ofelements needed in the feedback digital-to-analog converter circuit 212from 256 to 32.

FIG. 4 is a graph of an example of a simulation comparing outputspectrums. The x-axis represents frequency, and the y-axis representsspectrum in decibels (dB). The graph 300 compares a conventional 8-bitdelta-sigma ADC generating an in-band SQNR of 132 dB and a delta-sigmaADC using the techniques of this disclosure in FIG. 3 that includes an8-bit first quantizer and a 5-bit feedback digital-to-analog convertercircuit generating an in-band SQNR of 132 dB. Each ADC circuit was asecond order with an OSR of 64×. The band-of-interest is shown at 302(in-band), and the out-of-band is shown at 304.

The delta-sigma ADC techniques in FIG. 3 perform like the conventionaldelta-sigma ADC in-band, as indicated by their similar SQNRs. That is,the in-band noise of the delta-sigma ADC techniques of FIG. 3 isapproximately the same as the in-band noise of a conventionaldelta-sigma ADC with a quantizer and a feedback DAC as high resolutionas the first quantizer. The first quantizer, e.g., the first quantizer218 of FIG. 3 , dictates the in-band noise. The second quantizer, e.g.,the second quantizer 220 of FIG. 3 , dictates the out-of-band noise.

FIG. 5 is a graph of another example of a simulation comparing outputspectrums. The x-axis represents frequency, and the y-axis representsspectrum in decibels (dB). The graph 400 compares a conventional 5-bitdelta-sigma ADC generating an in-band SQNR of 119 dB and a delta-sigmaADC using the techniques of this disclosure in FIG. 3 that includes an8-bit first quantizer and a 5-bit feedback digital-to-analog convertercircuit generating an in-band SQNR of 132 dB. Each ADC circuit was asecond order with an OSR of 64×. The band-of-interest is shown at 402(in-band), and the out-of-band is shown at 404.

As shown in FIG. 5 , the in-band noise of the conventional delta-sigmaADC circuit is much higher than that of the delta-sigma ADC that usesthe techniques of FIG. 3 . The out-of-band noise for the delta-sigma ABCthat uses the techniques of FIG. 3 is similar to the out-of-band noiseof the conventional delta-sigma ADC circuit, as shown at 406. FIGS. 4and 5 graphically illustrate how the techniques of this disclosure canprovide independent control over in-band and out-of-band noise. In anextreme example, the first quantizer, e.g., the first quantizer 218 ofFIG. 3 , can be an 8-bit quantizer and the second quantizer, e.g., thesecond quantizer 220 of FIG. 3 , can be a 1-bit quantizer, such as aclass I) ADC. Simulations have shown that the in-band performance ofsuch a configuration having a second order and operated at an OSR of 128x can match the in-band performance of a conventional 8-bit delta-sigmaADC. Such a configuration can include a 1-bit feedback digital-to-analogconverter circuit, as compared to 8-bit feedback digital-to-analogconverter circuit that a conventional delta-sigma ADC would require.

In some examples, the filter F(z) of FIG. 3 can be a second orderfilter, such as 2z⁻¹−(z⁻²). A second order filter can provide secondorder shaping of the second quantizer, e.g., the second quantizer 220 ofFIG. 3 . By using a second order filter in the second quantizer loop,the requirement of the OSR for MQL can be reduced, such as from 64× to32× as mentioned above in order to match the performance of theconventional delta-sigma ADC.

The filter F(z) of FIG. 3 can be higher than second order. In someexamples, the filter F(z) of FIG. 3 and the excess loop delaycompensation circuit 228 of FIG. 3 , for example, can be implementedusing digital techniques. By using digital techniques, the order of thefilter and/or the coefficient of the gain block 232, for example, can beeasily changed to suit customer requirements, for example.

Referring to FIG. 3 , the output of the filter F(z) can be coupled tothe input of the second quantizer 220. However, in other examples, suchas shown in FIG. 6 , the output of the filter F(z) can be coupled to theinput of the first quantizer 218. In addition, the excess loop delaycompensation circuit 228 in FIG. 3 can be coupled to the input of thesecond quantizer 220. However, in other examples, such as shown in FIG.6 , the output of the excess loop delay compensation circuit can becombined with the output of the second quantizer and applied to thefilter coupled to the input of the feedback digital-to-analog convertercircuit.

FIG. 6 is a block diagram of another example of a delta-sigma ABCcircuit that can implement various techniques of this disclosure. In theexample shown, the circuit 500 can be a second order feed-forward loophaving a first integrator 502 and a second integrator 504. The firstintegrator 502 and the second integrator 504 can be continuous timeintegrators or discrete time integrators, e.g., switched capacitor-basedintegrators. The circuit 500 can receive an analog input signal 506 atan input 508, e.g., a buffer. An input summing node 510 can receive andcombine the analog input signal 506 and an output of a feedbackdigital-to-analog converter circuit 512.

The first integrator 502 can receive the output of the input summingnode 510 and perform an integration. The output of the first integrator502 can be applied to a gain block 514, and the output of the gain block514 can be combined with the output of the second integrator 504 by asumming node 516. The first integrator 502 and the second integrator 504form a second order loop filter. In other examples, there can be oneintegrator or more than two integrators. As such, the loop filter can beany order loop filter.

As mentioned above, the circuit 500 can include a first quantizer 518and a second quantizer 520. The first quantizer 518 can be coupled to anoutput of a summing node 521. The summing node 521 can receive theoutput of the summing node 516 and combine it with the output of afilter F(z), where the output of the summing node 516 can be arepresentation of the combined analog input signal 506 and output of thedigital-to-analog converter circuit 512. As such, the first quantizer518 can receive a representation of the combined analog input signal andoutput of the digital-to-analog converter circuit. In addition, and incontrast to FIG. 3 , an output of the filter F(z) can be applied to aninput of the first quantizer 518 in FIG. 6 . The first quantizer 518 cangenerate an output having a first number of bits. As a non-limitingexample, the first quantizer 518 can generate an output having 8-10bits.

The first quantizer 518 can dictate the in-band signal-to-quantizationnoise ratio (SQNR) of the circuit 500. In some examples, the firstquantizer 518 can be a flash ADC. In some examples, the first quantizer518 can be a successive approximation register (SAR) ADC circuit, suchas an asynchronous SAR ADC or a synchronous SAR ABC.

In accordance with this disclosure, the circuit 500 can further includea second quantizer 520 coupled to an output of the first quantizer 518to receive the output of the first quantizer 518. The second quantizer520 can generate an output having a second number of bits. In someexamples, the second number of bits is less than the first number ofbits. As a non-limiting example, the second quantizer 520 can generatean output having 4 or 5 bits.

In some examples, the second number of bits of the second quantizer 520can be less than the first number of bits of the first quantizer 518. Insome examples, the second quantizer 520 can implemented using digitaltechniques, such as a processor circuit, such as a digital signalprocessor circuit.

The input of the second quantizer 520 can be applied to a summing node524 and subtracted from the output of the second quantizer 520. Anoutput of the summing node 524 can be applied to a filter F(z), e.g., afinite impulse response (FIR) filter, which can then be fed to thesumming node 521 during the next clock cycle. The filter F(z) can be afirst order filter or a higher order filter. In some examples, thefilter F(z) can be a delay such as z⁻¹.

In some configurations in which the first quantizer 518 is a SAR ADC, anexcess loop delay compensation circuit 528 can be included. The excessloop delay compensation circuit 528 can include a filter 530, e.g., adelay such as z⁻¹, and a gain block 532, for example. The output of theexcess loop delay compensation circuit 528 can be fed to a loop delaysumming node 533 coupled to receive and combine the output of the excessloop delay compensation circuit 528 and the output of the secondquantizer 520, This technique of using a second quantizer 520 canre-quantize the output of the first quantizer 518 in order to reduce thenumber of bits applied to the feedback digital-to-analog convertercircuit 512. In this manner, the circuit 500 can include amulti-quantizer loop (MQL). Although two quantizers are shown, more thantwo quantizers can be used. In such a configuration, the number of bitscan be reduced in stages, such as from 8 bits to 5 bits to 3 bits usingthree quantizers.

The output of the summing node 533 can be fed to a filter 536, e.g., adelay, such as z⁻¹, such as in configurations in which the firstquantizer 518 is a SAR ADC. In addition, the output of the summing node533 can be applied to an output node 526 of the circuit 500 to provide adigital output of the delta-sigma ADC.

As an example, the filter 536 can provide one clock delay to emulate thedelay of a SAR ADC or for dynamic element matching. The filter 536 canbe coupled to an input of the feedback digital-to-analog convertercircuit 512. As a non-limiting example, the feedback digital-to-analogconverter circuit 512 can generate an output having 4 or 5 bits. In thismanner, the feedback digital-to-analog converter circuit 512 can becoupled to the second quantizer 520 to receive a representation of theoutput of the second quantizer 520, where the output of the feedbackdigital-to-analog converter circuit 512 has the second number of bits.

In some instances, the circuit 500 of FIG. 6 can be simpler to implementthan the circuit 200 of FIG. 3 , For example, in some instances it canbe simpler to add the output of the filter F(z) in the analog domain,such as by using the summing node 521 in FIG. 6 , as compared to theconfiguration of FIG. 3 .

NOTES

Each of the non-limiting aspects or examples described herein may standon its own or may be combined in various permutations or combinationswith one or more of the other examples.

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which theinvention may be practiced. These embodiments are also referred toherein as “examples.” Such examples may include elements in addition tothose shown or described. However, the present inventors alsocontemplate examples in which only those elements shown or described areprovided. Moreover, the present inventors also contemplate examplesusing any combination or permutation of those elements shown ordescribed (or one or more aspects thereof), either with respect to aparticular example (or one or more aspects thereof), or with respect toother examples (or one or more aspects thereof) shown or describedherein.

In the event of inconsistent usages between this document and anydocuments so incorporated by reference, the usage in this documentcontrols.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In this document, the terms “including” and “inwhich” are used as the plain-English equivalents of the respectivetennis “comprising” and “wherein.” Also, in the following claims, theterms “including” and “comprising” are open-ended, that is, a system,device, article, composition, formulation, or process that includeselements in addition to those listed after such a term in a claim arestill deemed to fall within the scope of that claim. Moreover, in thefollowing claims, the terms “first,” “second,” and “third,” etc. areused merely as labels, and are not intended to impose numericalrequirements on their objects.

Method examples described herein may be machine or computer-implementedat least in part. Some examples may include a computer-readable mediumor machine-readable medium encoded with instructions operable toconfigure an electronic device to perform methods as described in theabove examples. An implementation of such methods may include code, suchas microcode, assembly language code, a higher-level language code, orthe like. Such code may include computer readable instructions forperforming various methods. The code may form portions of computerprogram products. Further, in an example, the code may be tangiblystored on one or more volatile, non-transitory, or non-volatile tangiblecomputer-readable media, such as during execution or at other times.Examples of these tangible computer-readable media may include, but arenot limited to, hard disks, removable magnetic disks, removable opticaldisks (e.g., compact discs and digital video discs), magnetic cassettes,memory cards or sticks, random access memories (RAMs), read onlymemories (ROMs), and the like.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments may be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. § 1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Also, in the above Detailed Description,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the DetailedDescription as examples or embodiments, with each claim standing on itsown as a separate embodiment, and it is contemplated that suchembodiments may be combined with each other in various combinations orpermutations. The scope of the invention should be determined. Withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

The claimed invention is:
 1. A delta-sigma analog-to-digital convertercircuit to receive an analog input signal at an input and generate adigital output signal, the delta-sigma analog-to-digital convertercircuit comprising: an input summing node configured to receive andcombine the analog input signal and an output of a digital-to-analogconverter circuit; a first quantizer to receive a representation of thecombined analog input signal and output of the digital-to-analogconverter circuit, the first quantizer to generate an output having afirst number of bits; a second quantizer coupled to an output of thefirst quantizer to receive the output of the first quantizer, the secondquantizer to generate an output having a second number of bits; thedigital-to-analog converter circuit coupled to the second quantizer toreceive a representation of the output of the second quantizer, whereinthe output of the digital-to-analog converter circuit has the secondnumber of bits; and an output node coupled to the output of the secondquantizer, wherein the output node is configured to provide the digitaloutput signal, wherein the digital output signal has the second numberof bits.
 2. The delta-sigma analog-to-digital converter circuit of claim1, comprising: a filter to receive a difference between an input of thesecond quantizer and the output of the second quantizer.
 3. Thedelta-sigma analog-to-digital converter circuit of claim 2, wherein anoutput of the filter is applied to an input of the first quantizer. 4.The delta-sigma analog-to-digital converter circuit of claim 2, whereinan output of the filter is combined with the output of the firstquantizer.
 5. The delta-sigma analog-to-digital converter circuit ofclaim 1, comprising: an excess loop delay compensation circuit toreceive an output of the second quantizer and to compensate for a delayintroduced by the first quantizer.
 6. The delta-sigma analog-to-digitalconverter circuit of claim 5, comprising: a second quantizer summingnode to receive an output of the excess loop delay compensation circuit,an output of a filter, and the output of the first quantizer.
 7. Thedelta-sigma analog-to-digital converter circuit of claim 5, comprising:a loop delay summing node coupled to receive and combine the output ofthe excess loop delay compensation circuit and the output of the secondquantizer.
 8. The delta-sigma analog-to-digital converter circuit ofclaim 1, wherein the first quantizer includes a successive approximationregister (SAR) analog-to-digital converter.
 9. The delta-sigmaanalog-to-digital converter circuit of claim 1, wherein the secondnumber of bits is less than the first number of bits.
 10. A method ofoperating a delta-sigma analog-to-digital converter circuit to receivean analog input signal at an input and generate a digital output signal,the method comprising: receiving and combining, using an input summingnode, the analog input signal and an output of a digital-to-analogconverter circuit; receiving, using a first quantizer, a representationof the combined analog input signal and output of the digital-to-analogconverter circuit and generating an output having a first number ofbits; receiving, using a second quantizer coupled to an output of thefirst quantizer, the output of the first quantizer and generating anoutput having a second number of bits; and receiving, using thedigital-to-analog converter circuit coupled to the second quantizer, arepresentation of the output of the second quantizer, wherein the outputof the digital-to-analog converter circuit has the second number ofbits; and generating the digital output signal, wherein the digitaloutput signal has the second number of bits.
 11. The method of claim 10,comprising: receiving, using a filter, a difference between an input ofthe second quantizer and the output of the second quantizer.
 12. Themethod of claim 11, wherein the filter has an output, the methodcomprising: applying the output of the filter to an input of the firstquantizer.
 13. The method of claim 11, wherein the filter has an output,the method comprising: combining an output of the filter with the outputof the first quantizer.
 14. The method of claim 10, comprising:receiving, using an excess loop delay compensation circuit, an output ofthe second quantizer and to compensate for a delay introduced by thefirst quantizer.
 15. The method of claim 14, comprising: receiving,using a second quantizer summing node, an output of the excess loopdelay compensation circuit, an output of a filter, and the output of thefirst quantizer.
 16. The method of claim 14, comprising: receiving andcombining, using a loop delay summing node, the output of the excessloop delay compensation circuit and the output of the second quantizer.17. The method of claim 10, wherein receiving, using the firstquantizer, the representation of the combined analog input signal andoutput of the digital-to-analog converter circuit and generating theoutput having the first number of bits includes: receiving, using asuccessive approximation register (SAR) analog-to-digital converter, therepresentation of the combined analog input signal and output of thedigital-to-analog converter circuit and generating the output having thefirst number of bits.
 18. The method of claim 10, wherein the secondnumber of bits is less than the first number of bits.
 19. A delta-sigmaanalog-to-digital converter circuit to receive an analog input signal atan input and generate a digital output signal, the delta-sigmaanalog-to-digital converter circuit comprising: an input summing nodeconfigured to receive and combine the analog input signal and an outputof a digital-to-analog converter circuit; a successive approximationregister analog-to-digital converter to receive a representation of thecombined analog input signal and output of the digital-to-analogconverter circuit, the successive approximation registeranalog-to-digital converter to generate an output having a first numberof bits; a digital quantizer coupled to an output of the successiveapproximation register analog-to-digital converter to receive the outputof the successive approximation register analog-to-digital converter,the digital quantizer to generate an output having a second number ofbits; and the digital-to-analog converter circuit coupled to the digitalquantizer to receive a representation of the output of the digitalquantizer, wherein the output of the digital-to-analog converter circuithas the second number of bits.
 20. The delta-sigma analog-to-digitalconverter circuit of claim 19, comprising: an excess loop delaycompensation circuit to receive an output of the digital quantizer andto compensate for a delay introduced by the successive approximationregister analog-to-digital converter.